Method for continuously measuring melting steel temperature and measuring temperature pipe

ABSTRACT

The invention discloses a method for measuring the temperature of a molten steel continuously, comprises the following steps: providing a tube that is made of double bushings, both of the inner and outer bushings being close at one end and open at another end; putting the close end of the tube into the molten steel in such a way that the ratio of the length of the tube under the surface of the molten steel to the inner diameter of the inner bushing is equal or greater than 15 and the ratio of said length to the outer diameter of the outer bushing is greater than 3; connecting the open end of the tube with an infrared detector; and calculating the temperature of the molten steel through evaluating the radiation emitted by the inner bushing at the end that was put under the molten steel by means of the detector. A tube to implement the method is also disclosed.

TECHNICAL FIELD

[0001] The present invention relates to a method for measuring thetemperature of molten steel continuously and a tube used forimplementing said method.

BACKGROUND OF THE INVENTION

[0002] In metallurgy, the temperature of molten steel needs to bemeasured continuously. The steel making process is essentially theprocess of controlling the temperature and the ingredients of the moltensteel, so measuring the temperature of the molten steel continuously issignificant for improving productive efficiency, decreasing energyconsumption and improving quality. The conventional technique for themeasurement works in an object-contacted way. A platinum-rhodiumthermo-couple with a protector is put into the molten steel to sense thetemperature. However, the protector's lifetime is limited because of theerosion of steel residue and the thermo-couple is expensive, so the costof measurement is high, which is difficult to be accepted by steelmaking plants.

[0003] U.S. Pat. No. 3,432,522 discloses a device of continuouslymeasuring the temperature of molten steel, utilizing the blackbodycavity theory. According to this patent, a tube is put into the moltensteel and the temperature of the molten steel is obtained from theradiation emitted by the tube and received by an infrared detector.However, many disadvantages exist in this patent. Firstly, blackbodycavity is a special physical concept and physical model generatingstable spectral irradiation similar with that of the perfect blackbody.The radiant traits of a cavity depend on the structure, the material andother factors of the cavity, therefore, not every cavity can be calledas a blackbody cavity. This patent fails to describe the structure ofthe tube in detail and teach how deeply the tube should be put into themolten steel. Moreover, whether the ceramic portion of the tube shouldimmerge under the surface of the molten steel is not mentioned.Therefore, the tube in this patent should not be called as a blackbodycavity. Consequently, errors will occur in the results of themeasurement. Secondly, graphite used at the end of the tube is of strongvolatility under high temperature environment, and the volatile gas canpollute the optical path and significantly affect the accuracy of themeasurement.

SUMMARY OF THE INVENTION

[0004] The object of the invention is to provide a method and a tube formeasuring the temperature of molten steel continuously with low cost andhigh precision.

[0005] According to the invention, the method for measuring thetemperature of molten steel continuously comprises the following steps:providing a tube that is made of double bushings, both of the inner andouter bushings being close at one end and open at another end; puttingthe close end of the tube into the molten steel in such a way that theratio of the length of the tube under the surface of the molten steel tothe inner diameter of the inner bushing is equal or greater than 15 andthe ratio of said length to the outer diameter of the outer bushing isgreater than 3; connecting the open end of the tube with an infrareddetector; and calculating the temperature of the molten steel throughevaluating the radiation emitted by the inner bushing at the end thatwas put into the molten steel by means of the detector.

[0006] To implement the above method, the present invention provides atube, one end of which is configured to be put into molten steel tosense the temperature and another end of which is configured to beconnected with an infrared detector. The tube is made of doublebushings, both of the inner and outer bushings being close at one endand open at another end. The close end of the tube is put into themolten steel in such a way that the ratio of the length of the tubeunder the surface of the molten steel to the inner diameter of the innerbushing is equal or greater than 15 and the ratio of said length to theouter diameter of the outer bushing is greater than 3.

[0007] Based on heat transfer analysis and blackbody cavity theory,according to the invention, the structure of the tube and the length ofthe tube under the surface of the molten steel are specified so thatstable radiation of the blackbody cavity can be obtained. Accordingly,the temperature of the molten steel can be measured continuously withlow cost and high precision.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a schematic diagram of the device for measuring thetemperature of molten steel according to the method of the invention;and

[0009]FIG. 2 is a schematic diagram of the tube of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] As shown in FIG. 1, the device for measuring the temperature ofmolten steel continuously according to the method of the inventioncomprises a tube 6, an infrared detector 4, an optical fibre 3, a signalprocessor 1 and a computer 2. In operation, the tube 6 is fixed to aholder 5 and put into the molten steel 7. There is provided acone-shaped connector at the open end of the tube 6, in order to connectwith the infrared detector 4, in which a corresponding cone-shapedconcave is formed to facilitate replacing the tube.

[0011] Considering the tube has to be put into the molten steel, itshould be of excellent heat-resistance, molten steel scour-resistance,vibration-resistance, stability and accuracy. Therefore, the tube 6 ismade of double bushings, as shown in FIG. 2. Both of the inner bushing 8and the outer bushing 9 are close at one end and open at another end.The close end of the tube is put into the molten steel 7, and the openend is connected to the infrared detector 4 by a connector 10. The innerbushing 8 is preferably made from material of good heat-resistance andstability, such as Al₂O₃, with an inner diameter of, for example, 20 mm.The inner bushing 8 has the traits of good obturation andevaporation-resistance in high temperature environment, which ensurethat the optical path within the tube is clean and the measurementresults are accurate. The outer bushing 9 is preferably made frommaterial of good heat-resistance, erosion-resistance,oxidation-resistance and molten steel scour-resistance, such as Al₂O₃and C or Al₂O₃, C and Zr, with an outer diameter of, for example, 80 mm.Besides, in order to improve the measurement sensitivity, the outerbushing 9 is preferably thicker at the residue surface than at thetemperature measuring end. Furthermore, an oxidation-resistant coatingcan be applied to the outer bushing 9 and a protective bushing can befixed around it to improve stress intensity.

[0012] The process of measuring the temperature of the molten steel isbriefly described as follows. Firstly, putting the close end of the tube6 into the molten steel 7 in such a way that the ratio of the length ofthe tube under the surface of the molten steel to the inner diameter ofthe inner bushing is equal or greater than 15 and the ratio of saidlength to the outer diameter of the outer bushing is greater than 3. Ablackbody cavity is thus produced within the tube 6, which emitsinfrared radiation. The radiation is received by the infrared detector4. The received signals are transferred to the signal processor 1 andthe computer 2 through the optical fibre 3. The computer 2 calculatesthe effective emissivity of the cavity based on on-line blackbody cavitytheory and thus determines the temperature of the molten steel.

[0013] The structure of the infrared detector 4 and how to calculate thetemperature of the molten steel from the received infrared radiationbelong to the prior art, and, therefore, are not described here indetail.

[0014] The experimental results show that the measuring error is lessthan ±3° C.

[0015] It is emphasized that the above embodiment should not beunderstood as a limitation to the protection scope of the invention. Inthe invention, the key points are that the tube is made of doublebushings and the ratios of the length of the tube under the surface ofthe molten steel to the inner diameter and the outer diameter shouldsatisfy the conditions as set forth above. Any modifications orvariations within the spirit of the invention should be within theprotection scope of the invention.

1. A method for measuring the temperature of molten steel continuously,comprises the following steps: providing a tube that is made of doublebushings, both of the inner and outer bushings being close at one endand open at another end; putting the close end of the tube into themolten steel in such a way that the ratio of the length of the tubeunder the surface of the molten steel to the inner diameter of the innerbushing is equal or greater than 15 and the ratio of said length to theouter diameter of the outer bushing is greater than 3; connecting theopen end of the tube with an infrared detector; and calculating thetemperature of the molten steel through evaluating the radiation emittedby the inner bushing at the end that was put into the molten steel bymeans of the detector.
 2. The method according to claim 1, wherein thetube is connected to the detector through a cone-shaped connector. 3.The method according to claim 1, wherein the inner bushing is made frommaterial of good heat-resistance and stability.
 4. The method accordingto claim 3, wherein the inner bushing is made from Al₂O₃.
 5. The methodaccording to claim 1, wherein the outer bushing is made from material ofgood heat-resistance, erosion-resistance, oxidation-resistance andmolten steel scour-resistance.
 6. The method according to claim 1,wherein the outer bushing is thicker at the residue surface than at thetemperature measuring end.
 7. The method according to claim 1, whereinthe outer bushing is applied with an oxidation-resistant coating.
 8. Atube for measuring the temperature of molten steel continuously, one endof which is configured to be put into the molten steel to sense thetemperature and another end of which is configured to be connected withan infrared detector, wherein, the tube is made of double bushings, bothof the inner and outer bushings being close at one end and open atanother end, and the close end of the tube is put into the molten steelin such a way that the ratio of the length of the tube under the surfaceof the molten steel to the inner diameter of the inner bushing is equalor greater than 15 and the ratio of said length to the outer diameter ofthe outer bushing is greater than
 3. 9. The tube according to claim 8,wherein the inner bushing is made from material of good heat-resistanceand stability.
 10. The tube according to claim 9, wherein the innerbushing is made from Al₂O₃.
 11. The tube according to claim 8, whereinthe outer bushing is made from material of good heat-resistance,erosion-resistance, oxidation-resistance and molten steelscour-resistance.
 12. The tube according to claim 8, wherein the outerbushing is thicker at the residue surface than at the temperaturemeasuring end.
 13. The tube according to claim 1, wherein the outerbushing is applied with an oxidation-resistant coating.